Middle-of-Rack Switch Layout for Short Passive Server Links
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Solution Overview
Problem
Current server rack configurations face challenges in supporting higher data rates due to issues with passive cable assemblies exceeding 2.5 meters, requiring forward error correction, which increases energy consumption, and QSFP connections being insufficient for higher speed passive cable links.
Innovation Solution
Implementing a Middle of the Rack (MOR) switch connected to compute nodes with shorter cables and an Electrical to Optical Panel (EOP) to manage thermal energy and improve communication paths, using next-gen connectors for higher data rates and reducing cable lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If passive cable assemblies longer than 2.5 meters are used to connect TOR switch to compute nodes, then the cable length is sufficient for rack depth, but forward error correction is required which increases energy consumption
Solution Approach 1:
The patent divides the single long cable connection into two segments: a shorter passive cable from the compute node to the MOR switch, and an active optical connection from the MOR switch to the TOR switch. This segmentation allows the passive cable to remain under 2.5 meters (avoiding FEC requirements) while still supporting deep rack configurations through the intermediate MOR switch.
Solution Approach 2:
The MOR switch acts as an intermediary device between the compute nodes and the TOR switch. It receives signals from compute nodes via short passive cables and retransmits them via active optical connections to the TOR switch, enabling long-range communication without requiring long passive cables that would need FEC.
2Speed
If QSFP connectors are used for high-speed connections, then data rate capability is improved, but the connectors are insufficient for higher speed passive cable links exceeding 2.5 meters
Solution Approach 1:
The connection path is segmented into two parts with different connector types: QSFP connectors for the short passive cable links (maintaining high data rates), and active optical interfaces at the MOR switch for the longer transmission distances (ensuring reliability without FEC).
Solution Approach 2:
Different connector types and transmission modes are applied locally to different segments of the connection path: passive copper QSFP connectors for short distances where they provide sufficient bandwidth, and active optical interfaces for longer distances where they provide the necessary reliability and error correction capabilities.
3Device complexity
If all compute nodes are connected to a single TOR switch, then connection simplicity is maintained, but bandwidth oversubscription occurs between the switch and spine
Solution Approach 1:
The patent segments the switching function across two devices: the MOR switch handles local compute node connections and aggregation, while the TOR switch handles uplink connections to the spine. This segmentation distributes the bandwidth burden and eliminates the oversubscription problem at the TOR switch-spine interface.
Solution Approach 2:
The patent introduces an additional dimension to the network topology by adding the MOR switch as an intermediate layer between compute nodes and the TOR switch. This creates a two-tier switching architecture that improves bandwidth utilization by providing multiple aggregation paths and reducing concentration of traffic at the TOR switch.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces energy consumption by eliminating the need for forward error correction, supports higher data rates without oversubscription, and enhances thermal management and flexibility in communication paths.
Implementation Method 1
The MOR switch can be directly connected to optical cables or can be connected to an electrical to optical panel (EOP) that allows for conversion of the electrical signals to optical signals
Data Source
AI summary
A server rack with a plurality of compute nodes is positioned in a facility that includes a spine and the server rack includes a middle of rack ((OR) switch located near the middle of the server rack, vertically speaking. The MOR switch includes a plurality of ports that are connected via passive cables to the compute nodes provided in the server rack. In an embodiment the passive cables are configured to function at 56 Gbps using non-return to zero (NRZ) encoding and each cable may be about of less than 1.5 meters long. An electrical to optical panel (EOP) can be positioned adjacent a top of the server rack and the EOP includes connections to the MOR switch and to the spine, thus the EOP helps connect the MOR switch to the spine. Connections between adjacent server racks can provide for additional compute bandwidth when needed.